This error may occur when working with the Map Control 8.1 on Windows XP:
"Run-time error '429': You do not have an appropriate license to run this functionality."
This error is returned when the initial Windows XP user account tries to make use of the Map Control, and the License Manager has only a single ArcGIS floating license available.
Add the initial user to the Windows Users group. This group is part of the Administrators group. To modify the User Accounts, double-click the icon in Control Panel. Refer to Windows XP help for more details on adding users and user accounts.
The error will no longer occur if you subsequently add other users to the Users group, nor if you remove the initial user.